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Fully articulated rotor systems normally have ______ or more blades.
three
In a fully articulated rotor system, the blades are attached to the main rotor hub through a ______ hinge.
drag or lag
A semirigid rotor system uses ______ blades which are rigidly attached to the main rotor hub.
two
The main rotor hub in a semirigid rotor system is free to tilt and rock independently of the main rotor shaft, on what is known as a ______ hinge.
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Twisting a rotor blade causes it to produce a more even amount of ______ along its span.
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The pitch angle is the angle between the blade chord and a reference plane determined by the ______ hub.
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A rotor's angle of attack is the angle between the rotor's chord and the relative wind, and should not be confused with the relative pitch ______.
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Disk loading of a helicopter is the ratio of weight to the total main rotor ______ area.
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Helicopter lift can also be stated in terms of ______ third law of motion, as the downwash created behind the moving rotor blades creates an equal and opposite reaction force upward
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The principles applied to the venturi are also utilized to create lift for a helicopter. However, in lieu of a venturi, rotor blades with an airfoil shape are used to create a pressure differential in the air. The principles used by fixed-wing aircraft are also utilized to create lift for a helicopter. In the helicopter's case, rotor blades with an airfoil shape are used to create the ______ principle, air accelerated or increases in velocity as it flows over the top of an airfoil shape.
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The combination of the reduced pressure above the blade and the increased pressure below the blade provide the ______ that allows helicopters to fly.
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As with fixed wing aircraft, these pressure differences create a downwash below and behind the airfoil. Helicopter lift can also be stated in terms of ______ third law of motion, as the downwash created behind the moving rotor blades creates an equal and opposite reaction force upward.
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Coriolis effect causes the ______ or deceleration of the rotor blade as a result of the blade's centre of mass moving closer to or further from the axis of rotation.
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A vertical hinge, sometime called the ______ hinge, is incorporated into fully articulated rotor systems to accommodate this blade acceleration/deceleration.
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Autorotation is the state of flight where the main rotor system is being turned by the action of the relative wind passing up through the disc, rather than ______ power.
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Like airplanes, helicopters have a vertical, lateral, and ______ axis that pass through the centre of gravity.
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By using the antitorque pedals mounted on the floor of the cabin, a pilot can increase or decrease tail rotor thrust by changing the ______ of the tail rotor blades.
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Applying pressure to the right pedal decreases the ______ of the tail rotor blades and, therefore, decreases the amount of thrust produced.
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Applying pressure to the left pedal increases the ______ and increases the thrust produced.
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A helicopter with a single main rotor system requires the incorporation of an anti-torque system to overcome the ______, or tendency, of the helicopter to turn in the direction opposite the main rotor.
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A helicopter may have an anti-torque rotor, a fenestron (fan-in-tail design system), or a no-tail rotor (NOTAR) system to overcome the ______ of the main rotor.
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The ______ angle of a rotor blade is the angle between the blade chord line and a reference plane, whereas the angle of attack is the angle between the rotor's chord and the relative wind.
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Translating tendency is the tendency of a helicopter to drift towards the ______ because of the horizontal thrust produced by the tail rotor.
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Ground effect occurs when hovering near the ______.
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When the helicopter accelerates to an airspeed of approximately 15 miles per hour, a rapid increase in excess power develops, as evidenced by a transient induced aerodynamic vibration. This building of excess power is called ______.
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As the helicopter moves through the air, the relative airflow through the main rotor disc is different on the ______ side than on the retreating side.
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the ______ barked
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the ______ meowed
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Drag is the force which opposes helicopter movement. The total drag acts parallel to the relative wind in a direction opposite the helicopter's movement. You learned earlier that there are two main types of drag - induced and ______.
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Components of the helicopter, such as the cabin, rotor mast, tail, and landing gear, contribute to ______ drag.
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Thrust like lift is generated by the rotation of the main rotor system. In a helicopter, thrust can be forward, rearward, sideward, or ______.
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Once a helicopter leaves the ground, it is supported by the four aerodynamic forces. In this section, we will examine these forces as they relate to a helicopter in flight. Hovering For standardization purposes, this discussion assumes a stationary hover in a no-wild condition. During hovering flight, the variable forces are directed to make the helicopter preform as needed/ While hovering, the amount of main rotor thrust is changed to maintain the desired hover altitude. This is done by changing the angle of attack of the main rotor blades and by varying power, as needed. In this case, thrust acts in the same vertical direction as lift. To maintain a hover at a constant altitude, enough lift and thrust must be generated to equal the weight of the helicopter and the ______ produced by the rotor blades.
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______ is the distance from the rotor hub to the blade tip.
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Twisting a rotor blade causes it to produce a more even amount of ____ along its span.
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Disk loading of a helicopter is the ratio of weight to the total main rotor ____ area.
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The pitch angle is the angle between the blade chord and a reference plane determined by the rotor _____.
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Rotor blades with an airfoil shape are used to create the ______ principle, air accelerated or increases in velocity as it flows over the top of an airfoil shape.
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A vertical hinge, sometime called the ______ hinge, is incorporated into fully articulated rotor systems to accommodate this blade acceleration/deceleration.
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The pitch ______ is the ______ between the blade chord line and a reference plane, whereas the ______ of attack is the ______ between the rotor's chord and the relative wind.
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Autorotation is the state of flight where the main rotor system is being turned by the action of the relative wind passing up through the disc, rather than ______ power.
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During hovering flight, the variable forces are directed to make the helicopter perform as needed. While hovering, the amount of main rotor thrust is changed to maintain the desired hover altitude. This is done by changing the angle of attack of the main rotor blades and by varying power, as needed. In this case, thrust acts in the same vertical direction as lift. To maintain a hover at a constant altitude, enough lift and thrust must be generated to equal the weight of the helicopter and the ______ produced by the rotor blades.
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Like airplanes, helicopters have a vertical, lateral, and ______ axis that pass through the centre of gravity.
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Which major component of a helicopter is responsible for generating power to drive the main rotor system?
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Components of the helicopter, such as the cabin, rotor mast, tail, and landing gear, contribute to ______ drag.
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Study Notes
Rotor System Types and Features
- Fully articulated rotor systems typically feature four or more blades.
- In fully articulated systems, blades are attached to the main rotor hub through a vertical hinge.
- Semirigid rotor systems utilize two blades that are rigidly connected to the main rotor hub.
- The main rotor hub in semirigid systems tilts and rocks independently using a semi-rigid hinge.
Rotor Blade Dynamics
- Twisting a rotor blade results in a more uniform lift distribution along its span.
- Pitch angle is the angle between the blade chord and a reference plane defined by the rotor hub.
- Angle of attack signifies the angle between the rotor's chord and the relative wind; do not confuse it with relative pitch.
Disk Loading and Lift Generation
- Disk loading refers to the ratio of helicopter weight to total main rotor area.
- Lift generation can be explained using Newton's third law of motion, as the downward airflow creates an upward reaction force.
- Venturi principles are utilized in helicopter lift with airfoil-shaped rotor blades to create pressure differentials.
Pressure Differences and Downwash
- Rotor blades accelerate air, thereby creating reduced pressure above and increased pressure below the blade, enabling flight.
- Pressure differences generate downwash below and behind the airfoil.
Effects of Rotor Blade Movement
- The Coriolis effect impacts rotor blade acceleration/deceleration as the blade's center of mass changes distance from the axis of rotation.
- A vertical hinge in fully articulated rotor systems accommodates this adjustment.
Autorotation and Axis of Helicopter
- Autorotation occurs when the main rotor system is turned by the relative wind, rather than by engine power.
- Helicopters possess vertical, lateral, and longitudinal axes through their center of gravity.
Tail Rotor and Anti-Torque Mechanisms
- Antitorque pedals allow pilots to modify tail rotor thrust by adjusting blade pitch.
- Pressure on the right pedal reduces tail rotor thrust, while pressure on the left pedal increases it.
- A single main rotor helicopter necessitates an anti-torque system to counteract torque rotational tendencies.
Translating Tendency and Ground Effect
- Translating tendency is the tendency for helicopters to drift toward the tail rotor due to horizontal thrust.
- Ground effect enhances lift during hover when near the surface.
Drag Forces
- Drag opposes helicopter motion and is defined in two main types: induced and profile drag.
- Components of the helicopter contribute to profile drag by offering resistance to airflow.
Thrust and Aerodynamic Forces
- Thrust can be directed forward, rearward, sideward, or upward through rotor rotation.
- In hovering, thrust must equal helicopter weight and any induced drag produced by the rotor blades.
Aerodynamics in Hovering
- Changes in rotor thrust maintain desired altitude by adjusting blade angle of attack and varying engine power.
- Rotor hub's distance to blade tip is crucial for lift generation.
Summary of Key Concepts
- The pitch angle differentiates from angle of attack, focused on rotor dynamics.
- Understanding the various axes and forces allows pilots better control and maneuverability of helicopters.
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Description
Test your knowledge about the components and design of helicopters in this informative quiz. Learn about the airframe, cabin, landing gear, main rotor system, transmission, power plant, and tail rotor system. Challenge yourself and become a helicopter expert!
